The present invention relates to protective coating for aircraft and other applications, and more particularly to coatings for the protection of surfaces including features, such as fastener head patterns, that flex or work in service.
It has been the general practice in protective coating systems to apply a primer to the structure or surface to be protected, followed by a topcoat. In protective coating systems for structures having high stress areas such as exterior fastener head patterns, such as high speed aircraft, it has been the general practice to apply, between application of the primer and the topcoat, a flexible sealant over such areas or patterns to relieve the flexing stresses that would otherwise cause the topcoat to crack, thus exposing the underlying metal or surface to environmental attack. The sealant, such as is disclosed in MIL-S-81733, is capable of withstanding strain at low temperatures, such as is experienced by the skin of high speed aircraft, in order to keep the coating from cracking around aircraft fastener heads. The primer alone does not have the flexibility to provide this protection. However, this three-coating system has not provided the needed flexibility at extreme low temperatures under high altitude flight conditions to prevent cracking in high stress areas. Furthermore, the sealant takes a considerable amount of time to apply and does not have sufficient tensile strength, adhesion, toughness, flexibility, or corrosion inhibitive properties to function without a primer coat. In addition, the need to apply three coats, one over the other, adds complexity and is time consuming.